[screen] round 3 notes

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

fktry/data/validate.test.ts

@@ -1,17 +1,19 @@
 /**
- * LANE-DATA territory (the one file this lane owns inside src/sim/).
+ * LANE-DATA territory. Lives beside the JSON it guards (round 3: moved out of
+ * src/sim/, which returns fully to LANE-SIM).
+ *
  * Validates data/*.json against the contracts. It is the handshake that keeps five
  * parallel lanes from drowning in dangling ids: if a lane references a machine,
  * recipe, item or tech that data doesn't define, this test names it.
  */
 import { describe, expect, it } from 'vitest';
-import type { CommissionDef, ItemDef, MachineDef, MachineKind, RecipeDef, TechDef } from '../contracts';
+import type { CommissionDef, ItemDef, MachineDef, MachineKind, RecipeDef, TechDef } from '../src/contracts';
 
-import itemsJson from '../../data/items.json';
-import machinesJson from '../../data/machines.json';
-import recipesJson from '../../data/recipes.json';
-import techJson from '../../data/tech.json';
-import commissionsJson from '../../data/commissions.json';
+import itemsJson from './items.json';
+import machinesJson from './machines.json';
+import recipesJson from './recipes.json';
+import techJson from './tech.json';
+import commissionsJson from './commissions.json';
 
 const items = itemsJson as unknown as ItemDef[];
 const machines = machinesJson as unknown as MachineDef[];

fktry/lanes/LANE-SCREEN.md

@@ -222,3 +222,79 @@ NEXT (not self-assigning): stamps currently say the item's NAME; once MODELBEAST
 rather stamp the item's *silhouette* in its chip colour. Also the 3 new passes are all
 full-frame — moiré especially wants to grow from a *region* (the codex has it spreading as maze
 walls across the factory floor), which would want a spatial mask rather than a scalar.
+
+### Round 3 — 2026-07-17 — Opus 4.8
+
+SHIPPED: all 4 orders. Thank you for the v3 grant — `frame(timeMs, snap?)` is exactly the seam
+strain needed.
+- `strain.ts` (new) — pure, snapshot-shaped, no DOM/GL. The whole point: order 4's sterile
+  guarantee is now a unit test, not a promise.
+- `strain.test.ts` (new) — 14 tests. Screen suite is 44 green.
+- `glitchStack.ts` — `growthMask()` + tremor/fever warps + regional moiré + fever tint.
+- `index.ts` — snapshot peek, strain easing, deterministic moiré seed, 3-frame scram.
+
+DECISIONS:
+- **Tremor is measured in SECONDS, not units.** Your v3 units ruling made this: `stored` is
+  bandwidth-seconds, `draw-gen` is bandwidth/second, so `stored/(draw-gen)` is literally *how
+  long until the lights go out*. Dread ramps over the last 8 seconds of reserve. This falls out
+  correct at every scale for free — a megafactory bleeding 1000/s with 4000 banked feels exactly
+  as doomed as a shack bleeding 10/s with 40 banked, because both have 4 seconds. There's a test
+  pinning that equivalence. Raw `stored` would have made big factories look permanently calm.
+- **Surplus is always calm, whatever the reserve.** If `draw <= gen` nothing is draining, so
+  there is nothing to dread — which is *also* what makes the boot state (gen=draw=stored=0)
+  sterile by construction rather than by special-case. Order 4 fell out of the maths.
+- **Fever averages only the machines that run hot** (heat > 0.01). Averaging across every entity
+  would drown one glowing decoder in a sea of cold belts, and belts are most of a factory.
+- Tremor ≈ ¼ of the brownout's judder amplitude, and fever is a smooth sine haze while tremor is
+  random judder — so dread, fever and seizure are three distinguishable readings, not one dial.
+  Strain stays weather: MAD vs sterile is ~6.8, against ~35 for moiré. Subordinate as ordered.
+- **Regional moiré separates AREA from INTENSITY.** Intensity saturates early (`u_moire*2.2`
+  clamped) while the mask's radius keeps growing with tally. That's what makes a big shipment
+  read as "the maze has spread" instead of "everything got slightly shimmery" — which is the
+  whole difference between regional and a scalar fade.
+- `growthMask(p, seed, grow)` is written as the **reusable spatial-artifact template** you asked
+  me to note: an fbm-ragged growth front, aspect-corrected, creeping outward from a seed. Any
+  future artifact that should grow from a PLACE multiplies its amount by it. The raggedness is
+  load-bearing — a clean circle reads as a spotlight, not as spreading crystal.
+- Moiré seeds from the tick of the first moire-weighted shipment, so a given run always grows the
+  same maze while different runs grow it elsewhere. Debug-hook ships default to tick 0.
+
+VERIFIED (fixture snapshots + pixel reads + contact sheets):
+- **Order 4, at the pixel level**: rendered no-snapshot / boot / healthy at an *identical*
+  timebase — boot and healthy are **byte-for-byte identical** to no-snapshot. Strain cannot leak
+  into the NOTHING IS WRONG era. (First attempt showed MAD ~1-2 and that was my harness: each run
+  advanced the clock, so the *timecode digits* differed. Fixed the test, not the code.)
+- **Tremor ramp** (deficit 10/s): 20s left → 0, 8s (the horizon) → 0, 4s → 0.50, 2s → 0.75,
+  empty → 1.00. Fever 0.837 from hot decoders with tremor still 0.
+- **Regional moiré growth**, as % of frame taken over: 0 → 20.1% → 44.7% → 74.5% → 84.5% → 85.8%
+  across 0/4/10/25/60/150 crystals. It spreads; it does not switch. The front is visibly ragged.
+- **Seed**: same tick → same seed twice over; different tick → different seed. Deterministic.
+- **Scram**: read the bar's row per frame — `BAR,BAR,BAR,-,-,-`. Exactly 3 frames, readable now.
+- **Budget: 0.072 ms/frame** wall-clock with a forced GPU sync, on a 2000-entity factory with
+  every artifact class lit — `computeStrain`'s per-frame entity walk is not measurable at that
+  size. CPU-only 0.043 ms. Still ~28× under.
+
+BLOCKED/BROKEN: nothing outstanding.
+- **I found and fixed a real bug in my own code while chasing a false alarm.** My `dt` was
+  `Math.min(0.1, ...)` — ceiling clamped, floor not. A *negative* dt (clock rewind) turns
+  `ease()`'s `1-exp(-dt/tau)` into a huge negative multiplier and threw strain to **-3614** before
+  it crawled back. Production can't hit it (`performance.now()` is monotonic, and main.ts passes
+  it straight through), so this was only reachable from my harness — but an eased value that can
+  explode on a clock hiccup is a landmine, so `dt` is now clamped at both ends. Worth other lanes
+  checking their own dt handling if they ease anything.
+- Full suite went 215/216 once mid-run, then 216/216 twice — another lane mid-write, not a real
+  red. HEAD is clean repo-wide, tsc included.
+
+CONTRACT REQUEST: none. v3 covers everything I need.
+
+PROPOSAL: `SimSnapshot.bandwidth` has no *capacity* field, so THE SCREEN can express "seconds
+until empty" but not "the tanks are 20% full". Seconds is the better dread metric and I'd keep it
+either way — but if buffer capacity ever lands in the snapshot cheaply, a second reading ("reserve
+low" vs "reserve draining fast") would let strain distinguish a factory that's coasting on fumes
+from one that's falling off a cliff. Not asking; noting the seam while it's fresh.
+
+NEXT (not self-assigning): the mask template is ready for reuse — **bloom loops** and **HF dust
+piles** are the obvious next spatial artifacts (both are regional in the codex), and the strata
+biomes in §1 would suggest a mask per era. Also, now that strain reads the snapshot, THE SCREEN
+could react to `jammed` entities (a stalled factory *should* look bored — the feed drifting back
+toward clean is a nice punishment), but that's a design call, not a lane call.

fktry/src/screen/glitchStack.ts

@@ -29,6 +29,8 @@ uniform float t;
 uniform float u_mosh, u_melt, u_chroma, u_tear, u_roll, u_burn, u_noise, u_freeze;
 uniform float u_block, u_ring, u_moire;
 uniform float u_drift, u_brownout, u_flash;
+uniform float u_strain, u_fever;
+uniform vec2 u_moireSeed;
 uniform sampler2D u_stampTex, u_scramTex;
 uniform float u_stampAmt, u_stampScale, u_scram, u_scramY;
 
@@ -41,6 +43,21 @@ float vnoise(vec2 p){
 float fbm(vec2 p){ return 0.5*vnoise(p)+0.25*vnoise(p*2.3)+0.125*vnoise(p*5.1); }
 float lu(vec3 c){ return dot(c, vec3(0.299,0.587,0.114)); }
 
+// REUSABLE SPATIAL-ARTIFACT TEMPLATE (round 2 proposal, round 3 build).
+// An irregular growth front creeping outward from the seed point. grow=0 is nothing, grow=1 has
+// swallowed the frame. The fbm term makes the front ragged and organic instead of a
+// tidy circle, so the artifact spreads like the codex's maze walls rather than a spotlight.
+// Any future artifact that should GROW FROM A PLACE rather than fade in everywhere should
+// multiply its amount by this.
+float growthMask(vec2 p, vec2 seed, float grow){
+  vec2 d = p - seed;
+  d.x *= 1.78;                             // 16:9 correction: grow circles, not ellipses
+  float r = length(d);
+  float ragged = (fbm(d*3.2 + seed*7.0) - 0.5) * 0.38;
+  float front = grow * 1.35;               // reach past the corners at grow=1
+  return smoothstep(front + 0.10, front - 0.10, r + ragged);
+}
+
 void main(){
   // freeze quantizes the timebase everything else animates on.
   // A brownout slams the whole timebase into a hard stutter regardless of freeze.
@@ -51,6 +68,20 @@ void main(){
   // slow drift of the clean feed: bounded sinusoid, so no wrap seam
   uv += vec2(sin(t*0.07)*0.004, cos(t*0.05)*0.003) * u_drift;
 
+  // signal strain: the reserve is draining. A tremor, not a seizure — deliberately about a
+  // quarter of the brownout's amplitude, so dread reads as dread and the brownout still lands.
+  if(u_strain > 0.001){
+    float js = floor(tt*9.0);
+    uv.x += (hash(vec2(js, 17.0))-0.5) * u_strain * 0.017;
+    uv.y += (hash(vec2(js, 23.0))-0.5) * u_strain * 0.011;
+  }
+
+  // fever: the decoders are running hot. Slow heat-haze shimmer, no judder.
+  if(u_fever > 0.001){
+    uv.x += sin(uv.y*38.0 + tt*1.7) * u_fever * 0.0045;
+    uv.y += sin(uv.x*26.0 + tt*1.1) * u_fever * 0.0030;
+  }
+
   // desync judder: the frame itself loses its footing during a brownout
   if(u_brownout > 0.001){
     float j = floor(tt*12.0);
@@ -125,15 +156,21 @@ void main(){
     col += (col - blur) * u_ring * 1.5;            // overshoot at the edge itself
   }
 
-  // ---- moire: two near-identical lattices beating against the sensor grid
+  // ---- moire: two near-identical lattices beating against the sensor grid.
+  // REGIONAL: the crystal GROWS from a seeded place and creeps outward with the tally, rather
+  // than fading in across the whole frame. Intensity saturates early while AREA keeps growing,
+  // so a big shipment reads as "the maze has spread", not "everything got slightly shimmery".
   if(u_moire > 0.001){
-    float ang = 0.06 + 0.02*sin(tt*0.07);
-    vec2 r = vec2(vUv.x*cos(ang)-vUv.y*sin(ang), vUv.x*sin(ang)+vUv.y*cos(ang));
-    float a = sin(vUv.x*640.0*0.55 + vUv.y*3.0);
-    float b = sin(r.x*640.0*0.575 + r.y*2.0 + tt*0.25);
-    float m = a*b;                                 // the beat: swirling maze lattice
-    vec3 sheen = 0.5+0.5*cos(6.2831*(vec3(0.0,0.33,0.67) + m*1.2 + tt*0.03));
-    col = mix(col, col*0.4 + sheen*0.7, u_moire*clamp(abs(m)*1.5, 0., 1.));
+    float mo = clamp(u_moire*2.2, 0.0, 1.0) * growthMask(vUv, u_moireSeed, u_moire);
+    if(mo > 0.001){
+      float ang = 0.06 + 0.02*sin(tt*0.07);
+      vec2 r = vec2(vUv.x*cos(ang)-vUv.y*sin(ang), vUv.x*sin(ang)+vUv.y*cos(ang));
+      float a = sin(vUv.x*640.0*0.55 + vUv.y*3.0);
+      float b = sin(r.x*640.0*0.575 + r.y*2.0 + tt*0.25);
+      float m = a*b;                                 // the beat: swirling maze lattice
+      vec3 sheen = 0.5+0.5*cos(6.2831*(vec3(0.0,0.33,0.67) + m*1.2 + tt*0.03));
+      col = mix(col, col*0.4 + sheen*0.7, mo*clamp(abs(m)*1.5, 0., 1.));
+    }
   }
 
   // static
@@ -161,6 +198,9 @@ void main(){
   col = mix(col, rim2, edge * (1.0 - smoothstep(0.05, 0.35, edge)) * 2.0 * u_burn);
   col = mix(col, vec3(0.02), smoothstep(0.3, 1.0, edge) * step(0.01, u_burn));
 
+  // fever runs warm: the picture itself develops a temperature
+  col = mix(col, col*vec3(1.12,0.98,0.88), u_fever*0.55);
+
   // faint scanlines for vibe (constant, not scored)
   col *= 0.92 + 0.08 * sin(vUv.y * 360.0 * 3.1415);
 
@@ -191,7 +231,7 @@ void main(){
 }`;
 
 type UniformKey =
-  | Param | 't' | 'drift' | 'brownout' | 'flash'
+  | Param | 't' | 'drift' | 'brownout' | 'flash' | 'strain' | 'fever' | 'moireSeed'
   | 'stampTex' | 'scramTex' | 'stampAmt' | 'stampScale' | 'scram' | 'scramY';
 
 export interface DrawState {
@@ -205,6 +245,12 @@ export interface DrawState {
   flash: number;
   /** nothing shipped yet — the clean feed still carries its chyron */
   idle: boolean;
+  /** 0..1 tremor from the draining bandwidth reserve (weather, not climate) */
+  strain: number;
+  /** 0..1 feverish shimmer from aggregate machine heat */
+  fever: number;
+  /** where the moire crystal grows from, in screen uv */
+  moireSeed: [number, number];
   /** 0..1 opacity of the shipment stamp */
   stampAmt: number;
   /** stamp size multiplier — bigger shipments stamp harder */
@@ -285,6 +331,9 @@ export function createGlitchStack(
   uni.drift = gl.getUniformLocation(prog, 'u_drift');
   uni.brownout = gl.getUniformLocation(prog, 'u_brownout');
   uni.flash = gl.getUniformLocation(prog, 'u_flash');
+  uni.strain = gl.getUniformLocation(prog, 'u_strain');
+  uni.fever = gl.getUniformLocation(prog, 'u_fever');
+  uni.moireSeed = gl.getUniformLocation(prog, 'u_moireSeed');
   uni.stampAmt = gl.getUniformLocation(prog, 'u_stampAmt');
   uni.stampScale = gl.getUniformLocation(prog, 'u_stampScale');
   uni.scram = gl.getUniformLocation(prog, 'u_scram');
@@ -299,7 +348,8 @@ export function createGlitchStack(
   gl.uniform1f(uni.drift, 1);
 
   return {
-    draw({ params, timeSec, drift, brownout, flash, idle, stampAmt, stampScale, scram, scramY, stampDirty }) {
+    draw({ params, timeSec, drift, brownout, flash, idle, strain, fever, moireSeed,
+           stampAmt, stampScale, scram, scramY, stampDirty }) {
       // Re-upload the clean feed only when it actually changed (timecode tick / chyron).
       if (base.update(timeSec * 1000, idle)) {
         gl.activeTexture(gl.TEXTURE0);
@@ -315,6 +365,9 @@ export function createGlitchStack(
       gl.uniform1f(uni.drift, drift);
       gl.uniform1f(uni.brownout, brownout);
       gl.uniform1f(uni.flash, flash);
+      gl.uniform1f(uni.strain, strain);
+      gl.uniform1f(uni.fever, fever);
+      gl.uniform2f(uni.moireSeed, moireSeed[0], moireSeed[1]);
       gl.uniform1f(uni.stampAmt, stampAmt);
       gl.uniform1f(uni.stampScale, stampScale);
       gl.uniform1f(uni.scram, scram ? 1 : 0);

fktry/src/screen/index.ts

@@ -9,12 +9,13 @@
  * have ever shipped decides the intensity. Shipments arrive as waves, not switches —
  * every param eases toward its target.
  */
-import type { GameData, ItemDef, ScreenFX, SimEvent } from '../contracts';
+import type { GameData, ItemDef, ScreenFX, SimEvent, SimSnapshot } from '../contracts';
 import { createBaseFeed } from './baseTexture';
 import { createGlitchStack, type GlitchStack } from './glitchStack';
 import { createOverlays } from './overlays';
-import { resolveLedger, unmappedItems, ESCALATION_ITEMS } from './corruptionMap';
+import { corruptionFor, resolveLedger, unmappedItems, ESCALATION_ITEMS } from './corruptionMap';
 import { PARAMS, ease, zeroParams, type ParamSet } from './params';
+import { computeStrain } from './strain';
 
 /** Seconds for a param to travel ~63% toward its target. Shipments feel like waves. */
 const EASE_TAU = 1.2;
@@ -29,9 +30,27 @@ const WOBBLE_RATE = [0.13, 0.19, 0.11, 0.23, 0.17, 0.29, 0.31, 0.07, 0.09, 0.37,
 const STAMP_LIFE = 0.4;
 /** A burst of shipments must not become a strobe: at most this many stamps wait their turn. */
 const STAMP_QUEUE_MAX = 2;
+/** Round 3: one frame was a flinch, not a legend. Three frames is readable. */
+const SCRAM_FRAMES = 3;
+/** Tremor tracks the reserve fairly tightly; fever is a slow burn. */
+const STRAIN_TAU = 0.35;
+const FEVER_TAU = 1.5;
 
 interface Stamp { name: string; count: number; color: string; age: number }
 
+/**
+ * Where the moire crystal takes root. Deterministic in the tick it first appeared, so a given
+ * run always grows the same maze, while different runs grow it somewhere else. Kept off the
+ * edges so the growth reads as spreading rather than creeping in from off-screen.
+ */
+function seedFromTick(tick: number): [number, number] {
+  const h = (n: number) => {
+    const x = Math.sin(n * 12.9898 + 78.233) * 43758.5453;
+    return x - Math.floor(x);
+  };
+  return [0.25 + h(tick + 1) * 0.5, 0.25 + h(tick + 99) * 0.5];
+}
+
 const clamp01 = (x: number) => Math.min(1, Math.max(0, x));
 function smoothstep(e0: number, e1: number, x: number): number {
   const t = clamp01((x - e0) / (e1 - e0));
@@ -59,9 +78,14 @@ export function createScreenFX(): ScreenFX {
   const stampQueue: Stamp[] = [];
   let stamp: Stamp | null = null;
   let stampDirty = false;
-  let pendingScram = false;
+  let scramFrames = 0;
   let scramY = 0.5;
 
+  let strain = 0;
+  let fever = 0;
+  let moireSeed: [number, number] = [0.5, 0.44];
+  let moireSeeded = false;
+
   let lastMs = 0;
   let frameCost = 0; // rolling avg ms of this module's CPU work
 
@@ -73,7 +97,7 @@ export function createScreenFX(): ScreenFX {
     ledgerDirty = false;
   }
 
-  function ship(item: string, count: number) {
+  function ship(item: string, count: number, tick = 0) {
     if (count <= 0) return;
     tally.set(item, (tally.get(item) ?? 0) + count);
     ledgerDirty = true;
@@ -81,6 +105,11 @@ export function createScreenFX(): ScreenFX {
       hasShipped = true;
       pendingFlash = true; // the awakening
     }
+    // The crystal takes root where and when it first arrived, and grows from there.
+    if (!moireSeeded && (corruptionFor(item).weights.moire ?? 0) > 0) {
+      moireSeed = seedFromTick(tick);
+      moireSeeded = true;
+    }
     // One stamp per EVENT, not per unit: a 40-unit shipment is one big stamp.
     const def = items.get(item);
     stampQueue.push({
@@ -111,19 +140,26 @@ export function createScreenFX(): ScreenFX {
       (window as any).__fktryScreen = {
         ship,
         brownout: (on: boolean) => (brownoutTarget = on ? 1 : 0),
-        scram: () => { pendingScram = true; scramY = 0.5; },
+        scram: () => { scramFrames = SCRAM_FRAMES; scramY = 0.5; },
         reset: () => {
           tally.clear();
           ledgerDirty = true;
           hasShipped = false;
           stamp = null;
           stampQueue.length = 0;
+          moireSeeded = false;
+          moireSeed = [0.5, 0.44];
+          strain = 0;
+          fever = 0;
           for (const p of PARAMS) eased[p] = 0;
         },
         stats: () => ({
           units: +units.toFixed(2),
           total: +total.toFixed(3),
           idle: !hasShipped,
+          strain: +strain.toFixed(3),
+          fever: +fever.toFixed(3),
+          moireSeed: moireSeed.map((n) => +n.toFixed(3)),
           brownout: +brownout.toFixed(2),
           msPerFrame: +frameCost.toFixed(3),
           tally: Object.fromEntries(tally),
@@ -135,26 +171,36 @@ export function createScreenFX(): ScreenFX {
 
     onEvents(events: SimEvent[]) {
       for (const e of events) {
-        if (e.kind === 'shipped') ship(e.item, e.count);
+        if (e.kind === 'shipped') ship(e.item, e.count, e.tick);
         else if (e.kind === 'brownout') brownoutTarget = e.on ? 1 : 0;
         else if (e.kind === 'scram' && e.on) {
           // A machine scrammed: the tape loses tracking. Bar position is derived from the
           // event rather than random, so the same run always wipes the same way.
-          pendingScram = true;
+          scramFrames = SCRAM_FRAMES;
           scramY = 0.15 + (((e.entity * 37 + e.tick * 13) % 100) / 100) * 0.7;
         }
       }
     },
 
-    frame(timeMs: number) {
+    frame(timeMs: number, snap?: SimSnapshot) {
       if (!stack) return;
       const t0 = performance.now();
-      const dt = lastMs === 0 ? 1 / 60 : Math.min(0.1, (timeMs - lastMs) / 1000);
+      // Clamp BOTH ends. A negative dt (clock rewind, a paused tab resuming oddly, a test
+      // harness restarting its timebase) turns ease()'s 1-exp(-dt/tau) into a huge negative
+      // multiplier and throws every eased value into orbit. The ceiling stops long stalls
+      // from snapping params; the floor stops that.
+      const dt = lastMs === 0 ? 1 / 60 : Math.min(0.1, Math.max(0, (timeMs - lastMs) / 1000));
       lastMs = timeMs;
 
       if (ledgerDirty) recompute();
       brownout = ease(brownout, brownoutTarget, dt, BROWNOUT_TAU);
 
+      // v3: read-only peek. Collapsed to two scalars immediately — the snapshot is never
+      // retained across frames, per the contract invariant.
+      const target = computeStrain(snap);
+      strain = ease(strain, target.tremor, dt, STRAIN_TAU);
+      fever = ease(fever, target.fever, dt, FEVER_TAU);
+
       const timeSec = timeMs / 1000;
       const wobble =
         total > WOBBLE_THRESHOLD ? (total - WOBBLE_THRESHOLD) / (1 - WOBBLE_THRESHOLD) : 0;
@@ -191,10 +237,11 @@ export function createScreenFX(): ScreenFX {
       const flash = pendingFlash ? 1 : 0;
       stack.draw({
         params: out, timeSec, drift: 1, brownout, flash, idle: !hasShipped,
-        stampAmt, stampScale, scram: pendingScram, scramY, stampDirty,
+        strain, fever, moireSeed,
+        stampAmt, stampScale, scram: scramFrames > 0, scramY, stampDirty,
       });
       pendingFlash = false;
-      pendingScram = false;
+      if (scramFrames > 0) scramFrames--;
       stampDirty = false;
 
       frameCost = frameCost * 0.95 + (performance.now() - t0) * 0.05;

fktry/src/screen/strain.test.ts

@@ -0,0 +1,101 @@
+import { describe, expect, it } from 'vitest';
+import type { EntityState, SimSnapshot } from '../contracts';
+import { computeStrain, STRAIN_HORIZON_SECONDS } from './strain';
+
+function snap(bandwidth: Partial<SimSnapshot['bandwidth']>, entities: Partial<EntityState>[] = []): SimSnapshot {
+  return {
+    tick: 0,
+    paused: false,
+    entities: entities.map((e, i) => ({
+      id: i, def: 'x', pos: { x: 0, y: 0 }, dir: 0, recipe: null, progress: 0,
+      inputBuf: {}, outputBuf: {}, jammed: null, heat: 0, ...e,
+    })),
+    beltItems: [],
+    bandwidth: { gen: 0, draw: 0, stored: 0, brownout: false, ...bandwidth },
+    shippedTotal: {},
+    activeCommission: null,
+    commissionProgress: {},
+  };
+}
+
+describe('the NOTHING IS WRONG era stays sterile', () => {
+  it('is inert with no snapshot at all', () => {
+    expect(computeStrain(undefined)).toEqual({ tremor: 0, fever: 0 });
+  });
+
+  it('does not leak strain into a fresh factory (gen=draw=stored=0)', () => {
+    // The boot state. Nothing built, nothing drawing: dread here would be a lie.
+    expect(computeStrain(snap({}))).toEqual({ tremor: 0, fever: 0 });
+  });
+
+  it('stays calm for a healthy factory running a surplus', () => {
+    expect(computeStrain(snap({ gen: 100, draw: 40, stored: 500 }))).toEqual({ tremor: 0, fever: 0 });
+  });
+
+  it('stays calm in surplus even with an empty reserve', () => {
+    // Nothing is draining, so there is nothing to dread — banked reserve is irrelevant.
+    expect(computeStrain(snap({ gen: 100, draw: 100, stored: 0 })).tremor).toBe(0);
+  });
+
+  it('stays calm with cold machines', () => {
+    expect(computeStrain(snap({ gen: 10, draw: 5 }, [{ heat: 0 }, { heat: 0 }])).fever).toBe(0);
+  });
+});
+
+describe('tremor tracks seconds-of-reserve, not raw stored', () => {
+  it('is silent while the reserve outlasts the horizon', () => {
+    // deficit 10/s, 200 banked = 20s of runway: further out than the horizon.
+    expect(computeStrain(snap({ gen: 0, draw: 10, stored: 200 })).tremor).toBe(0);
+  });
+
+  it('is total when the reserve is gone and the draw continues', () => {
+    expect(computeStrain(snap({ gen: 0, draw: 10, stored: 0 })).tremor).toBe(1);
+  });
+
+  it('sits halfway at half the horizon', () => {
+    const stored = 10 * (STRAIN_HORIZON_SECONDS / 2); // deficit 10/s -> horizon/2 seconds left
+    expect(computeStrain(snap({ gen: 0, draw: 10, stored })).tremor).toBeCloseTo(0.5, 5);
+  });
+
+  it('rises monotonically as the reserve drains', () => {
+    let prev = -1;
+    for (let stored = 200; stored >= 0; stored -= 10) {
+      const t = computeStrain(snap({ gen: 0, draw: 10, stored })).tremor;
+      expect(t).toBeGreaterThanOrEqual(prev);
+      prev = t;
+    }
+    expect(prev).toBe(1);
+  });
+
+  it('reads the same dread from a big factory as a small one at equal runway', () => {
+    // A megafactory bleeding 1000/s with 4000 banked is in exactly as much trouble as a
+    // shack bleeding 10/s with 40 banked. Seconds, not units, is the honest measure.
+    const big = computeStrain(snap({ gen: 0, draw: 1000, stored: 4000 })).tremor;
+    const small = computeStrain(snap({ gen: 0, draw: 10, stored: 40 })).tremor;
+    expect(big).toBeCloseTo(small, 5);
+  });
+
+  it('never leaves 0..1, even absurdly overdrawn', () => {
+    const t = computeStrain(snap({ gen: 0, draw: 1e9, stored: -50 })).tremor;
+    expect(t).toBeGreaterThanOrEqual(0);
+    expect(t).toBeLessThanOrEqual(1);
+  });
+});
+
+describe('fever reads the machines that actually run hot', () => {
+  it('is not diluted by a sea of cold belts', () => {
+    // One decoder at 0.9 surrounded by 50 cold belts is a fever, not a rounding error.
+    const entities = [{ heat: 0.9 }, ...Array.from({ length: 50 }, () => ({ heat: 0 }))];
+    expect(computeStrain(snap({}), ).fever).toBe(0);
+    expect(computeStrain(snap({}, entities)).fever).toBeCloseTo(0.9, 5);
+  });
+
+  it('averages across the hot machines', () => {
+    expect(computeStrain(snap({}, [{ heat: 0.4 }, { heat: 0.8 }])).fever).toBeCloseTo(0.6, 5);
+  });
+
+  it('stays within 0..1 for a fully scrammed factory', () => {
+    const f = computeStrain(snap({}, [{ heat: 1, scrammed: true }, { heat: 1 }])).fever;
+    expect(f).toBe(1);
+  });
+});

fktry/src/screen/strain.ts

@@ -0,0 +1,66 @@
+/**
+ * Signal strain — the continuous half of THE SCREEN's vocabulary.
+ *
+ * Events give edges (brownout on/off); the snapshot gives quantities. Strain is what the
+ * factory feels BEFORE the seizure: the reserve draining toward empty, the decoders running
+ * hot. Strain is weather; the corruption ledger is climate. It stays deliberately subordinate.
+ *
+ * Pure and snapshot-shaped on purpose: no DOM, no GL, so the "healthy factory stays sterile"
+ * guarantee is a unit test rather than a promise.
+ */
+import type { SimSnapshot } from '../contracts';
+
+export interface Strain {
+  /** 0..1 tremor/desync judder as the bandwidth reserve runs out */
+  tremor: number;
+  /** 0..1 slow feverish shimmer from aggregate machine heat */
+  fever: number;
+}
+
+export const NO_STRAIN: Strain = { tremor: 0, fever: 0 };
+
+/**
+ * How much runway counts as calm. Reserve deeper than this reads as healthy; dread ramps up
+ * as the factory's remaining seconds fall toward zero.
+ */
+export const STRAIN_HORIZON_SECONDS = 8;
+
+/** Machines idling at a trace of heat are not a fever. */
+const HEAT_FLOOR = 0.01;
+
+const clamp01 = (x: number) => Math.min(1, Math.max(0, x));
+
+/**
+ * Read-only peek at the snapshot (contracts v3). The snapshot is never retained: everything
+ * needed collapses to two scalars here and now.
+ */
+export function computeStrain(snap?: SimSnapshot): Strain {
+  if (!snap) return NO_STRAIN;
+
+  // --- tremor: seconds of reserve remaining at the current deficit.
+  // Per the v3 units ruling, `stored` is bandwidth-SECONDS while gen/draw are bandwidth per
+  // second — so stored/deficit is literally "how long until the lights go out".
+  const { gen, draw, stored } = snap.bandwidth;
+  const deficit = draw - gen;
+  let tremor = 0;
+  if (deficit > 0) {
+    const secondsLeft = Math.max(0, stored) / deficit;
+    tremor = 1 - clamp01(secondsLeft / STRAIN_HORIZON_SECONDS);
+  }
+  // A factory in surplus is calm no matter how little it has banked — that is what keeps
+  // strain out of the NOTHING IS WRONG era, where gen and draw are both zero.
+
+  // --- fever: how hot are the machines that actually run hot.
+  // Averaging across every entity would drown a glowing decoder in a sea of cold belts.
+  let sum = 0;
+  let hot = 0;
+  for (const e of snap.entities) {
+    if (e.heat > HEAT_FLOOR) {
+      sum += e.heat;
+      hot++;
+    }
+  }
+  const fever = hot > 0 ? clamp01(sum / hot) : 0;
+
+  return { tremor, fever };
+}